These do not differentiate tenax from other members of the genus; but what WLR means is that the looped vein in the wing points to Eristalis. The stigma is not important in an ID of Eristalis tenax, but can help with one or two of the other members of the genus, like E. interruptus.

The rows of hairs down the eye are the most obvious ID feature for tenax, on this specimen. As WLR hints, the broad face stripe is also indicative of tenax.